Enquiry of Ze from DNO.......useless!!

[kme]

Scott:

I know what our Albert is getting at.....

In order to measure the Ze, you have to physically disconnect the earthing conductor - yes?

especially with their being no bonding; you`d have intentionally removed the ONLY source of protective earthing for testing purposes, whilst part of the installation was powered up? Baaaaaaaaad idea, AFAIAC mate - and if there is a server being fed from this supply; its likely to be a switched-mode unit; which has inherent leakage anyway!!!!!

IF there is NO structural steel, and NO bonding, then a Zs reading shouldn`t be too far away from a Ze anyway? If you`re still worried; the customer declining a full shutdown automatically gives rise to a "lim" on Ze by measurement anyway......

Yes?

 

[S60TEM]

I know exactly what your saying guys 100%

The server that was running wasn't running any PC's as the school was closed for the holidays, it was just left on and all that was running was it's internal fans.

There was some sort of earth bonding if you class the pathetic SWA bonding to the water in the cellar room and the whole istallation was in metal trunking / SWA so there would still have been a path to earth if you catch my drift.

The Installation was under no load anywhere other than the spur for the server and the earth was disconnected for 20 seconds max.

There was nobody else on the premises other than myself and my brother in law who was with me at the time who could come to any risk due to there being no earth connected.

Hope that clarifies what the scenario was.

---------- Post Auto-Merged at 14:30 ---------- Previous post was made at 14:28 ----------

I just tried to be as thorough as possible with it being a primary school and as the DNO couldn't provide me with a Ze, I didn't want to put a LIM in the box

 

[steptoe]

Scott,

take this as you will, and think of me in whatever manner you want,

But,

that has to be one of the worst things I have ever heard anyone ever admit to in an internet forum,

you intentionally removed an earthing conductor from an installation that was still energised,

that is at best seriously bad judgement and veering into cowboy 5ww territory,

at worst, serious incompetence that could have killed someone of caused severe damage to equipment and plant/buildings.

IMHO.

---------- Post Auto-Merged at 17:40 ---------- Previous post was made at 17:38 ----------

I know exactly what your saying guys 100%The server that was running wasn't running any PC's as the school was closed for the holidays, it was just left on and all that was running was it's internal fans.

There was some sort of earth bonding if you class the pathetic SWA bonding to the water in the cellar room and the whole istallation was in metal trunking / SWA so there would still have been a path to earth if you catch my drift.

The Installation was under no load anywhere other than the spur for the server and the earth was disconnected for 20 seconds max.

There was nobody else on the premises other than myself and my brother in law who was with me at the time who could come to any risk due to there being no earth connected.

Hope that clarifies what the scenario was.

---------- Post Auto-Merged at 14:30 ---------- Previous post was made at 14:28 ----------

I just tried to be as thorough as possible with it being a primary school and as the DNO couldn't provide me with a Ze, I didn't want to put a LIM in the box

so it wouldnt be as bad then as the guy you killed was your B-i-L , thats OK then.

 

[Andy™]

Scott,take this as you will, and think of me in whatever manner you want,

But,

that has to be one of the worst things I have ever heard anyone ever admit to in an internet forum,

you intentionally removed an earthing conductor from an installation that was still energised,

that is at best seriously bad judgement and veering into cowboy 5ww territory,

at worst, serious incompetence that could have killed someone of caused severe damage to equipment and plant/buildings.

IMHO.

---------- Post Auto-Merged at 17:40 ---------- Previous post was made at 17:38 ----------

so it wouldnt be as bad then as the guy you killed was your B-i-L , thats OK then.

so what if he disconnected the earth whilst live? there was only him & one other in the building. only miminal circuits were connected. disconnecting the earth temporarily would not be a big risk, compared to full installation still energised and loads of people in the building.

 

[S60TEM]

So tell me how you get your measured Ze readings on the tests you do then because without actually having to have the instalation energised how can you do it? You need a connection to LINE, NEUTRAL and EARTH at the head.

The reason I contacted DNO is because I didn't want to disconnect it but I needed to check that the Supply authority earth fault loop impedance was present and within the 0.35 ohms a TNC-S system allows.

1) It couldn't have killed anyone because there was no one there to kill otherwise I wouldn't have disconnected it if the premises had people present.

2) There would have been NO damage to equipment as every distribution board was isolated and the one that wasn't the only MCB on was the 16A one that fed the spur for the server which in turn wasn't running as there was no PC's on at the time so if nothing was energised, how could they have produced a fault current to injure anyone or damage equipment if they were all isolated at submains?

I'm sorry but I resent the "Incompetance" and the "cowboy" remark !!

At NO time was there anyone at risk or any equipment at risk and for the one point of current using equipment that was energised, the installation was cross bonded everywhere because it was in metallic trunking and there was a bond to the water even if it was inadequate it would have carried the fault current IF the server had generated a fault imo!

---------- Post Auto-Merged at 18:19 ---------- Previous post was made at 18:13 ----------

[quote name='Andy

 

[steptoe]

lets all start using twin cable again then,

you obviously see no reason for the earth being present.

that is a total disregard for the regulations we are supposed to work under.

---------- Post Auto-Merged at 19:07 ---------- Previous post was made at 19:00 ----------

regulation 8 (Earthing and other suitable precautions) of EAWR specifically prohibits this, and EAWR is the LAW

regulation 29 (defence) would not be any use to you as you did not take 'all reasonable steps'

 

[M107]

Well personaly I'd have gone with a LIM on the Ze rather than disconnecting the MEC (as said a baaaaad idea, if you even hinted at the idea on an assessment you'd be failed there & then).

At a local school here I gave the caretaker a shout who called the head teacher who, after me explaining the problem & potential hazard & EAWR then authorised the purchase of a UPS & then came in to shut down the server, I did the Ze & circuit dead tests, then reconnected the server to UPS & the head rebooted the server.

Surprised me that a school didnt have a ups on the main server anyway...............as I said to the head what happens in the event of a power cut? that clinched the sale

 

[Manator]

Before we all go into free fall over this subject, lets all take a step back. Firstly when filling in the certificates we are given measured and enquired maximum Ze readings. If for any reason I can not disconnect the main earthing, I have two options of providing this reading, A) by enquiry or B) by recording with earthing attached and recorded on the schedule. You should never ever remove the main earthing for this test if the building is occupied. I have just got back from testing a five star hotel with over 800 rooms, and I will tell you there are more limitations to testing than you would ever want in a lifetime. The client is king and all you can do is show that doing say 20% of the installation will ultimately mean that we attend on a more frequent basis, and basically test on a rolling scheme , like painting the Forth road bridge.

Limitations are inbuilt into the system because in the real world it is not possible at all times to adhere to each regulation, but to achieve a compromise, which will accurately reflect the condition of the installation. safety of any persons on site is paramount.

 

[steptoe]

So tell me how you get your measured Ze readings on the tests you do then because without actually having to have the instalation energised how can you do it? You need a connection to LINE, NEUTRAL and EARTH at the head.

exactly, you have a L + E , you dont need a N to do a Ze, and you dont need the installation energised either,

in general I will test at the incoming side of the first isolator that I have access to,

I switch off the power, remove the cover to the isolator, disconnect the earthing conductor from the MET(or other convenient point that performs an earth isolation) and test,

re-connect the earthing conductor, replace the isolators cover, and energise.

simples.

anyone out there claiming to be a spark, and especially with a scheme membership shouldnt really need to be told how to test a Ze safely.

didnt you learn anything about safe isolation? maybe you should ask your scheme if they think your method was a safe way of testing Ze.

 

[Sidewinder]

Steps,

I actually removed the earthing from a live install druing an assessment visit following a RA and tested the Ze then refitted the earth.

With suitable safe isolation in the mean while.

THe AE was fine with this as I had done a suitable and sufficient RA, sorry mate but it can be done.

NOT by any and sundry as you MUST FULLY understand what the ramifications of your removing the earth are and what can be damaged and who can be killed!

This is the difficult bit!

It takes a deep understanding of the install, what is there, what will be re-energised and what the possible failure modes are.

 

[steptoe]

Sidewinder, I know it can be done, as can removing the N from a 3ph,(if everything is simply 3p balanced),

but, I dont think in this instance it was

A necessary

or

B done with any consideration of the potential pitfalls,

OP has stated it was fine cos no one else was in the building, I dont feel that in any way justifies this kind of action in these circumstances,

it was a totally un-necessary risk that I dont think you could ever justify in an RA.

 

[Sidewinder]

Quite Steps, there must be more to the RA then, oh the building is currently empty!

 

[S60TEM]

I think you's fail to see the point. I did do an RA or I wouldn't have got the contract without it. As it was a school, the whole building is always locked down at every entrance and because we were testing all over the school then we also had the deadlocks on the doors so nobody could get into the building without us knowing so I catagorically know that nobody was in the building and nobody could get into the building! Everybody jumping on the bandwagon again as if none of you's have ever worked live when we all know sometimes we have to!

What the difference is is beyond me that the isolator was on, yes but the whole installation other than one circuit was isolated. FFS what the difference between me putting my probes into the DB above the isolator thats live (because it was feeding the server) or in the LIVE open enclosure of the main isolator.........same amount of risk but actually LESS risk my way because there was only 230V present in the DB and as we all know there is 415V present inside the main isolator!

Nobody could have got a shock because the current using equipment (server) was ran off an UNSWITCHED spur so not as if mr phantom sneaker could have plugged anything in!!

Come on, yes we have to follow the rules and regs as best we can and 99.9% of the time i'm by the book etc and I'll make sure that not only am I safe but more importantly anyone (if anyone) else is safe also.

---------- Post Auto-Merged at 23:11 ---------- Previous post was made at 23:10 ----------

oh and for the record, the 3 lead method is by force of habit not necessity

 

[steptoe]

the very point is this,

you had an energised installation with current using equipment connected and you disconnected the earthing conductor,

its that simple,

a member on here recently got b0110cked for (alledgedly) cutting a seal, to isolate an installation, that was silly,

by comparison, what you did, was, IMHO, downright stupid/incompetent (delete as you feel appropriate).

so you didnt test the Ze on all 3phases then I assume.?

---------- Post Auto-Merged at 23:28 ---------- Previous post was made at 23:26 ----------

I still don't see why the server could not have been turned off to be honestIf its that important why wasnt it on a UPS anyway ?

apparently it wasnt even in use, just the fans running, :C

I dont know enough about them, but would agree with the UPS.

 

[steptoe]

oh, wouldnt they have been more efficent being wind powered? :slap

 

[S60TEM]

ha ha ha, very funny.

As for a UPS, I dunno why they hadn't one but I was instructed that the servers couldn't be turned off as it was something to do with rebooting and data loss. I did mention to the caretaker about what happens in a power cut and he said that they had to call in an IT company to come reboot the server! As you's, I don't know anything about servers etc etc so can't comment.

Maybe I'll consult you guys next time then eh when I'm next doing a PIR because obviously what I done has NEVER been done before in the history of Ze testing even though there was a 0% risk to any persons or equipment!

 

[ADS]

After all the argument and discussion and the 'cans' and 'can'ts' - Why didn't you just measure Ze with the 'Earthing Conductor' still connected? (You could have disconnected the 'water' clamp first if that bothered you.)

 

[steptoe]

ha ha ha, very funny.As for a UPS, I dunno why they hadn't one but I was instructed that the servers couldn't be turned off as it was something to do with rebooting and data loss. I did mention to the caretaker about what happens in a power cut and he said that they had to call in an IT company to come reboot the server! As you's, I don't know anything about servers etc etc so can't comment.

Maybe I'll consult you guys next time then eh when I'm next doing a PIR because obviously what I done has NEVER been done before in the history of Ze testing even though there was a 0% risk to any persons or equipment!

and herein lies the problem,

there wasnt 0% risk,

the risk may have been minimal, or maybe you just got lucky,

but did you put in your RA,

danger of electric shock = 0 ?

couldnt have been much to read then.

 

[ADS]

GN3 Pg 50 - Top Paragraph, Second Sentence

'The means of earthing must be disconnected from the installation earthed equipotential bonding for the duration of the test to remove parallel paths.'

As you stated that there wasn't any bonding (apart from an 'earth clamp' on the SWA armour to the water.....hardly what we'd call 'bonding'), I think you could safely say there weren't any parallel paths, so you could measure Ze without disconnecting the 'Earthing Conductor'

 

[kme]

OH!

I thought this thread may have reached a satisfactory conclusion yesterday......silly me.

Scott: If this course of action IS taken, without VERY special precautions and circumstances (as has been said; if the server was THAT important, it`d have a UPS), there is a risk associated. (Snakey: I know where you`re coming from, but I don`t think such specialised circumstances need to be introduced to this particular discussion.)

It simply isn`t done, mate. Either there is a "whoops! did I do that?" moment; or there happens to BE a power cut at the appropriate time (by design if necessary);or it is simply a LIM. "I don`t want to put a lim" isn`t sufficient cause, IMO, to disregard statutory laws.

If the client doesn`t want a lim in the box; they authorise server shutdown (possibly for the provision of a UPS - more